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Full text of "Superconducting ceramics in the Bi1.5SrCaCu2O sub x system by melt quenching technique"

NASA Contractor Report 185139 



Superconducting Ceramics in the 
Bii.5SrCaCu20x System by 
Melt Quenching Technique 



Narottam P. Bansal and Mark R. DeGuire 

Case Western Reserve University 
Cleveland, Ohio 



October 1989 



Prepared for 

Lewis Research Center 

Under Cooperative Agreement NCC3-133 



fWNSA 



National Aeronautics and 
Space Administration 

(NASA-CR-185139) SUPERCONDUCTING CERAMICS N90-il606 

IN THP Pil.5SrCaCu20 SUP x SYSTEM BY MfcLT 

QUENCHING TFCHNlQUfc Final Report (Case unclas 

western Reserve Univ.) 20 o CSCL 20L ^^^^^ uncl-^ 



SUPERCONDUCTING CERAMICS IN THE Bii , 5SrCaCU20x SYSTEM 
BY KELT QUENCHING TECHNIQUE 

Narottam P. Bansal* and Mark R. DeGuiret 

Case Western Reserve University 

Department of Material Science and Engineering 

Cleveland, Ohio 44106 

SUMMARY 

Bii,5SrCaCu20x has been prepared in the glassy state by rapid 
quenching of the melt. The kinetics of crystallization of various 
phases in the glass have been evaluated by a variable heating rate 
differential scanning calorimetry method. The formation of various 
phases on thermal treatments of the glass has been investigated by 
powder x-ray diffraction and electrical resistivity measurements. 
Heating at 450^0 formed Bi2Sr2Cu06, which disappeared on further 
heating at 7650c, where Bi2Sr2CaCU208 formed. Prolonged heating at 
8450C resulted in the formation of a small amount of a phase with 
Tc onset of ~108K, believed to be Bi2Sr2Ca2CU30io. This specimen 
showed zero resistivity at 54K. The glass ceramic approach could 
offer several advantages in the fabrication of the high-T^ 
superconductors in desired practical shapes such as continuous 
fibers, wires, tapes, etc. 



*NASA Resident Research Associate at Lewis Research Center 
+Summer Faculty Fellow. 



INTRODUCTION 

The formation of superconducting cercimics via the melt 
quenching and glass -ceramic route would allow well established 
glass manufacturing techniques to be used for commercial oxide 
superconductor fabrication. Precipitation of Y-Ba-Cu-0 
superconductors from oxide glasses containing B2O3 and other glass 
formers has been tried without much success^. Since 81203 is 
known^ to be a reasonably good glass former, the discovery of 
superconductivity in the Bi-Sr-Ca-Cu-O system by Maeda et al.-^ 
makes it a promising choice for fabrication of superconducting 
materials by the glass ceramic route. Several groups^"^ have 
characterized and studied the formation of superconducting phases 
in glasses of this system. The present work focuses on the 
kinetics of crystallization of both superconducting and 
non-superconducting compounds in the Bi-Sr-Ca-Cu-0 glass, and the 
thermal treatments needed to increase the fraction of the high-T^ 
superconducting phase. 

EXPERIMENTAL METHODS 

Reagent grade 61203, CaC03, SrC03 , and CuO were mixed in 
stoichiometric amounts to yield "ISg of Bi^^ 5SrCaCu20x. The 
mixture was heated in a covered Pt crucible to 830°C for Ih to 
decompose the carbonates and then melted and kept at 1300°C for 2h 
for homogeneization of the melt. The melt was rapidly quenched by 
pouring onto a steel plate and covering with another similar steel 



plate. This resulted into opaque sheets of glass <lniin thick. 
Regions of black and bronze colored crystals were evident on the 
top and bottom surfaces of the glass sheets. The crystallite 
regions did not extend appreciably into the bulk. Powder x-ray 
diffraction (XRD) pattern of these sheets was characteristic of 
glass. XRD patterns were recorded at room temperature with Cu Ka 
radiation in the 29 range 10 - 80° using a Philips ADP 3600 
automated dif fractometer equipped with a crystal monochroraator . 
Chemical analysis of the glass was carried out using atomic 
absorption technique. The batch and analyzed weight % of various 
elements in the as-quenched glass were Bi(46.9, 47.3), Sr(13.1, 
13.7), Ca(6.0, 6.2), and Cu(19.0, 18.3) indicating no material 
loss during the glass melting. 

Thermogravimetric analysis (TGA) was carried out using a 
Perkin-Elmer TGS-2 system. Differential thermal analysis (DTA) and 
differential scanning calorimetry (DSC) were performed to 
determine the glass transition and crystallization temperatures, 
using the Perkin-Elmer DTA 1500 and DSC-4 interfaced with 
computerized data acquisition and analysis systems. Using a 
kinetic model of Bansal et al.^, the kinetics of crystallization 
of various phases formed during thermal treatment were determined 
via a variable heating rate DSC method employing scan rates of 2 - 
40°C/min. Several heat treatments were conducted based on the 
thermal events observed in the DTA and DSC, and the crystalline 
phases present after each treatment were identified by powder XRD. 



The superconducting transition temperature (T^,) of some of these 
devitrified specimens was determined using four-point electrical 
resistivity measurements. Microstructures of the crystallized 
samples were observed in a scanning electron microscope (SEM). 

RESULTS AND DISCUSSION 
Thermal Analyses 

The DTA thermogram of the fast quenched Bi^ . 5SrCaCu20x glass 
recorded at a heating rate of 10°C/min in air is shown in Fig. 1. 
A number of peaks are present. The glass transition is observed at 
390°C, a sharp crystallization exotherm at ~453°C followed by a 
broad peak between 540 and 585°C. A strong melting endotherm is 
present between 840 - 890°C followed by weak peaks at 899 and 
94°C which may be assigned to the melting of minor crystalline 
phases. 

The DSC trace of a BiSrCaCu20x glass^ is very similar to the 
low-temperature region of Fig. 1. On a glass of the same nominal 
composition as reported here, Komatsu et al.^ observed 
crystallization peaks of similar magnitude, but at 40 - 50°C 
higher temperature. There are several possible reasons for this 
discrepancy: (1) Their glasses may have contained some alumina 
from the crucibles in which they were melted, which could reduce 
the tendency to devitrification; (2) The present glass samples 



showed some surface crystallization after quenching as well as 
after brief heating suggesting that surface nucleation may have 
lowered the crystallization temperatures in the present work. 

Komatsu et al.^ also observed a broad endotherm at 768°C that 
is absent in Fig. 1. These workers concluded that the 768°C 
transformation was crucial to the formation of a high-temperature 
superconducting phase. Although this transition was not observed 
in the present work, Bi2Sr2CaCu208 phase was present in samples 
heated in this range, as discussed below. 

The DSC trace of the glass recorded at a scan rate of 10°C/min 
in air is presented in Fig. 2. The exotherms which appeared as 
single peaks in the DTA (Fig. 1) have split up into double peaks 
in the DSC. This probably indicates simultaneous crystallization 
of multiple phases on heat treatment of the glass. A variable 
heating rate DSC method was used to evaluate the kinetics of 
crystallization of various phases in the glass. DSC scans were 
recorded at heating rates of 2, 5, 10, 20, 30, and 40Oc/min. The 
positions of various peaks at various scan rates are listed in 
Table I. The peak positions are seen to shift to higher 
temperatures with increase in heating rate. The kinetic parameters 
were evaluated using a kinetic model of Bansal et al.^ which is 
expressed as: 



ln[T 2/a] = ln(E/R) - In »/ + E/RTp (1) 



where Tp is the peak maximum temperature, a is the heating rate, E 
the activation energy, R the gas constant, and v the frequency- 
factor. Eq. (1) is an extension of the Johnson-Mehl-Avrami 
isothermal kinetic model for use in non-isothermal methods. In the 
derivation of eq.(l) it has been assumed that the rate of reaction 
is maximum at the peak, which is valid for a power-compensated 
DSC. It has been demonstrated in earlier studies^' ^^ that the 
kinetic parameters determined from non-isothermal DSC using eq.(l) 
are in excellent agreement with those derived from the isothermal 
method. Plots of ln[Tp2/a] vs. 1/Tp for the four DSC peaks are 
shown in Fig. 3. The lines are from linear least-squares fitting. 
All the plots are linear indicating applicability of the kinetic 
model of Bansal et al^. Values of the kinetic parameters for the 
processes corresponding to the four DSC peaks were evaluated from 
linear least-squares fitting of the data of Table I and the 
results are listed in Table II. The values of activation energy 
for three of the processes are about the same. The reason for this 
is not clear at this point. 

TGA of a glass sample heated at 5°C/min to 850°C followed by 
cooling at the same rate is shown in Fig. 4. The entire cycle of 
heating and cooling was carried out in flowing oxygen. The sample 
weight remains unaltered upto ~500°C followed by a slow and 
continuous weight gain to ~800°C. The maximum gain in sample 
weight is ~1.7%. This probably results from oxidation of Cu and/or 
Bi. On cooling, almost no change in sample weight is observed 



indicating an irreversible oxidation step during heating. A high 
Cu oxidation state is a common feature of the high-T,-. compounds. 
The evidence of oxidation in Fig. 4 indicates that an oxidation 
step may be necessary for forming high-T^ phases from 
melt-processed Bi-Sr-Ca-Cu-0 materials. 

XRD Analysis of Crystallization Events 

The quenched glass samples were subjected to various thermal 
treatments as shown in Table III. The heat treatment temperatures 
were chosen from the positions of various peaks in the DTA 
thermogram. The various phases formed in these heat treated 
specimens were identified from powder XRD. Typical powder XRD 
patterns are shown in Fig. 5 and 6 and the results are summarized 
in Table III. Bi2Sr2Cu06^^ was the predominant crystalline phase 
observed in samples A, D, and B with intensities increasing from A 
to B to D. In addition, three samples contained diffraction peaks 
at 0.290, 0.246, and 0.240 nm. These peaks approximately doubled 
in intensity from sample A to samples B and D, but maintained 
constant intensities relative to each other in all these three 
samples. These observations suggest that these peaks arise from a 
single unidentified phase, which first crystallized near 450°C. It 
was not possible to determine whether this phase formed before or 
after Bi2Sr2CuOg, but the appearance of two closely spaced 
exothermic events near 450°C in the DSC is consistent with the 
formation of two distinct phases. The exothermic peaks near 560°C 



appear to be related to the disappearance of a phase with an XRD 
reflection at 0.175nm and/or the appearance of a phase with 
reflections at 0.219 and 0.177nni. 

Heating at 765°C (samples C and E, Table III) resulted in the 
diminishitient of Bi2Sr2Cu06 and the appearance of Bi2Sr2CaCu20g and 
CuO as major phases. The Bi2Sr2CaCu20g lattice was a few percent 
larger compared to the XRD data of Torrance et al.^^ In addition, 
a moderately strong peak at 0.388 nra was observed in these 
Scimples, as well as a very weak 0.244 nm peak which is 
characteristic of an unidentified phase. 

Heating for a few days at 845°C (samples F and G, Table III) 
yielded Bi2Sr2CaCu20g as a major phase, Bi2Sr2Cu06 as a minor 
phase, the 0.244 nra phase (weakly), and CuO as a trace phase. The 
Bi2Sr2Cu05 peaks were noticeably stronger in the fast-cooled 
sample, suggesting that upon slow cooling from 845°C the 
Bi2Sr2CuOg reacts with residual glass, CuO, and/or the 
unidentified crystalline phases to form more Bi2Sr2CaCu20g. This 
is consistent with early reports that the higher-T^ phases in this 
system become unstable with respect to the lower-T(;, phases as the 
temperature increases toward the melting point^^. The weak 
presence of CuO in these samples contrasts with the 765°C samples, 
but it is not clear what role the CuO formation around 765°C may 
play in the crystallization of Bi2Sr2CaCU208, such as nucleating 
the superconducting phase or perhaps being consumed during its 
formation. Refections at 0.369 and 0.262 nm, which have been 



associated with the llOK Bi-Sr-Ca-Cu-0 superconducting phase^, 
were not observed, although a small resistance drop near llOK was 
observed in the slow-cooled sample (vide infra). 

SEM Microstructures 

The SEM micrograph of the fracture surface of the specimen 
heated at 450Oc for 2h is presented in Fig. 7. The crystals appear 
to nucleate at the surface and grow into the bulk of the sample. 
Fig. 8 shows the SEM micrographs from two different regions of the 
same sample annealed for 2h each at 450 and 560Oc and slow cooled. 
Crystallization is not yet complete as seen from the presence of 
glassy regions in the sample. 

Electrical Resistivity Measurements 

The plots of electrical resistivity as a function of 
temperature for the samples annealed at 165^0 and above are 
presented in Figs. 9 and 10 and the results for all the specimens 
are summarized in Table IV. All four samples exhibited a sharp 
drop in resistance between 82 and 88K, consistent with the XRD 
results showing the presence of Bi2Sr2CaCu208, which has been 
previously identified ^^ as the 80K superconducting phase. In most 
other respects, however, the resistivity behavior of these 
specimens differs appreciably. The 2h heated samples (C and E, 
Table IV) showed broad superconducting transitions, reaching zero 
resistance at 47 and 38K respectively. Sample E (765°C, 2h) 



displayed semiconducting behavior in the normal state, whereas 
sample C, which was brought to the annealing temperature in 
stages, showed nearly flat behavior from 90 to 300K. The XRD 
traces of these specimens were virtually identical, however. The 
high-T^ oxides typically exhibit metallic normal state behavior 
when single phase, indicating that the above-transition 
resistivity of these samples is strongly influenced by the 
non-superconducting crystalline and glassy phases that are still 
major components after 2 - 6h of annealing. 

Samples heated at 845°C for 88h (F and G, Table IV) consisted 
mostly of Bi2Sr2CaCU208, but their resistivity behavior differed 
strongly with their post-annealing cooling schedules. The 
fast-cooled sample showed strong semiconducting behavior in the 
normal state. After a sharp drop in resistance at 88K, its 
resistivity leveled off, dropped again around 50K, and did not 
reach zero until IIK. The slow-cooled specimen, in contrast, 
showed metallic normal state behavior, a small drop in resistivity 
at ~108K, a major drop at 87K, and the highest zero-resistivity T,-, 
in this work (55K). In conjunction with the XRD findings that the 
slow-cooled sample contained less Bi2Sr2CuOg than the fast-cooled, 
these results qualitatively support reports that the higher-T^ 
phases (Bi2Sr2CaCU208, Bi2Sr2Ca2CU30iQ ) form from and on the 
surface of grains of the lower-Tj, phases-^^. It should be repeated. 



10 



however, that no Bi2Sr2Ca2Cu30io was detected in the XRD traces of 
these samples, despite the 108K resistivity drop in the 
slow-cooled sample. 

Shi et al.^ have shown that zero resistivity can be obtained 
at 105K in a glass sample of nominal composition Bi2Sr2Ca3Cu40x 
after heating at 870°C for a week. Bansal and Farrell^^ have also 
observed T^lR = 0) of 107. 2K in a glass ceramic of starting 
composition Bi^^ sPbg . 5Sr2Ca2CU30x which had been annealed at 840°C 
for more than 10 days. These results indicate very slow reaction 
kinetics for the formation of the 108K phase, probably due to the 
long range diffusive ordering involved. 

SUMMARY AND CONCLUSIONS 

Bii^5SrCaCu20x glass, prepared by rapid quenching of the melt, 
had a Tg of 390°C, crystallization temperature of ~450°C, and 
melting temperature of ~878°C. On heating in air, a slow and 
irreversible gain in weight (~1.7%) is observed probably due to 
oxidation of the material. Kinetic parameters for the 
crystallization of various phases in the parent glass have been 
evaluated from a variable heating rate DSC method. On thermal 
annealing a number of phases crystallized out from the glass. All 
glass-ceramic samples were multiphase. Bi2Sr2CuOg was the main 
crystalline phase in samples heated at >560°C. Bi2Sr2CaCu208 
appeared in specimens annealed at >765°C. High-T^ phase, probably 
Bi2Sr2Ca2Cu3O]^0, was formed on extended heating at 845°C 



11 



indicating slow kinetics. Furnace cooled samples showed higher T^. 
than those air-quenched after annealing under identical 
conditions. Obtaining practical superconducting materials via the 
glass precursor route will require tailoring the starting 
composition and thermal treatments to eliminate or minimize the 
effects of the non- superconducting phases and devising approaches 
with more favorable rapid crystallization kinetics. 

ACKNOWLEDGMENTS 

Thanks are due to Ralph Garlick for the X-ray diffraction 
measurements and Ann Waters for the thermal analyses. Nancy 
Gilbert assisted with the SEM work as a NASA summer intern. We are 
grateful to Professor D. E. Farrell for the electrical resistivity 
measurements. This work was supported by a NASA/ASEE summer 
faculty fellowship to Mark De Quire. 



12 



REFERENCES 

1. A. Bhargava, A. K. Varshneya, and R. L. Snyder, 
"Crystallization of Glasses in the System BaO-Y^03-B203" , 
Proceedings of the Conference on Superconductivity and 
Applications, Buffalo, NY, April 1988. 

2. G. W. Morey, "The Properties of Glass", 2nd ed. , Van Nostrand, 
New York, 1954. 

3. H. Maeda, Y. Tanaka, M. Fukutorni, and T. Asano, "A New High 
Tp Oxide Superconductor Without Rare Earth Element", Jpn. J. 
Appl. Phys., 27[2], L209-L210 (1988). 

4. T. Komatsu, R. Sato, K. Imai, K. Matsusita, and T. Yamashita, 
"High-T(^ Superconducting Glass Ceramics Based on the 
Bi-Ca-Sr-Cu-0 System", Jpn. J. Appl. Phys., 27[4], L550-L552 
(1988). 

5. V. Skumryev, R. Puzniak, N. Karpe, Z. Han, M. Pont, H. 
Medelius, D.-X. Chen, and K. V. Rao, "Physical Properties of 
BiiCaiSriCuoOx Superconductor Obtained by Rapid Quenching from 
the Melt"^, Physica C, 152, 315-320 (1988). 

6. D. Shi, M. Blank, M. Patel, D. G. Hinks, A. W. Mitchell, K. 
Vandervoort, and H. Claus, "llOK Superconductivity in 
Crystallized Bi-Sr-Ca-Cu-0 Glasses", Physica C, 156[5], 
822-826 (1988). 

7. A. Inoue, H. Kimura, K. Matsuzaki, A. P. Tsai, and T. 
Masumoto, "Production of Bi-Sr-Ca-Cu-0 Glasses by Liquid 
Quenching and Their Glass Transition and Structural 
Relaxation", Jpn. J. Appl. Phys., 27[6], L941-L943 (1988). 

8. N. P. Bansal and R. H. Doremus, "Determination of Reaction 
Kinetics Parameters from Variable Temperature DSC or DTA" , J. 
Thermal Anal., 29[1], 115-119 (1984). 

9. N. P. Bansal, A. J. Bruce, R. H. Doremus, and C. T. Moynihan, 
"The Influence of Glass Composition on the Crystal Growth 
Kinetics of Heavy Metal Fluoride Glasses", J. Non-Cryst. 
Solids, 70[3], 379-396 (1985). 

10. N. P. Bansal, R. H. Doremus, A. J. Bruce, and C. T. Moynihan, 
"Kinetics of Crystallization of ZrF4-BaF2-LaF3 Glass by 
Differential Scanning Calorimetry" , J. Am. Ceram. Soc, 66[4], 
233-238 (1983). 

11. J. B. Torrance, Y. Tokura, S. J. LaPlaca, T. C. Huang, R. J. 
Savoy, and A. I. Nazzal, "New Class of High T^ Structures: 



13 



Intergrowth of Multiple Copper Oxide Perovskite Layers with 
Double Sheets of BiO", Solid St. Commun. , 66, 703-708 (1988). 

12. M. R. De Guire, V. Finan, and N. P. Bansal, "The Series 
Bi2Sr2Caij-iCUj^Oy (l<.n <.5): Phase Relations and 
Superconductivity", Paper Presented at the 91st Annual Mtg. 

of the American Ceramic Society, Indianapolis, IN, April 1989. 

13. M. A. Subraraanian, C. C. Torardi, J. C. Calabrese, J. 
Gopalakrishnan, K. J. Morrissey, T. R. Askew, R. B. Flippen, 
U. Chowdhry, and A. W. Sleight, "A New High-Temperature 
Superconductor: Bi2Sr3_xCaxCU208+y" , Science, 239, 1015-1017 
(1988). 

14. J. M. Tarascon, Y. LePage, P. Barboux, B. G. Bagley, L. H. 
Greene, W. R. McKinnon, G. W. Hull, M. Giroud, and D. M. 
Hwang, "Crystal Substructure and Physical Properties of the 
Superconducting Phase Bi4(Sr,Ca)gCu4026+x"' Phys. Rev. B37, 
9382-9389 (1988). 

15. N. P. Bansal and D. E. Farrell, "Glass-Derived Superconducting 
Ceramics With Zero Resistance at 107K in the 

Bi]^ 5Pbo.5Sr2Ca2Cu30x System", Appl. Phys. Lett., in press. 



TABLE I. - DSC PEAK MAXIMUM TEMPERATURES AT VARIOUS 
HEATING RATES FOR THE 81 i . 5SrCaCu20x GLASS 



Heating 
rate, 

a, 
"C/mln 


Tg. 

'C 


Maximum peak temperature, °C 


Peak 1 


Peak 2 


Peak 3 


Peak 4 


2 


— 


433 


449 


539 


553 


5 


— 


441 


458 


555 


567 


10 


390 


450 


462 


562 


579 


20 


392 


460 





575 


592 


30 


395 


465 


— 


583 


— 


40 


398 


478 


— 


589 


— 


40 


402 


482 


— 


590 


— 



TABLE II. - KINETIC PARAMETERS FOR THE FORM- 
ATION OF VARIOUS CRYSTALLINE PHASES IN 
B1i.5SrCaCu20x GLASS, EVALUATED FROM 
NON-ISOTHERMAL DSC 



DSC 
peak 


Activation 
energy, 

E. 
kJ/mol 


Frequency 
factor, 

V, 

s-1 


Correlation 
coefficient 


1 


347 


1 .4xl023 


0.995 


2 


458 


4.8xl030 


.986 


3 


333 


S.Sxlo'S 


.995 


4 


334 


2. 6x10^8 


.999 



14 



TABLE III. - CRYSTALLINE PHASES IDENTIFIED FROM POWDER X-RAY DIFFRACTION IN 
B1i.5SrCaCU20x GLASS SAMPLES ANNEALED AT VARIOUS TEMPERATURES IN AIR 



Sample 



C 

D 

E 
F 



Heat treatment 



Temper- 
ature, 
°C 



450 



450 
560 

450 
560 
765 

560 



765 
845 

845 



Time, 
h 



2 
2 

2 
2 
2 



2 
88 



Cooling 



Slow 

^Slow 

Slow 

Slow 

Slow 
Quenched 

Slow 



Phases; d(nm) of unidentified lines 



Bl2Sr2Cu06; 0.29, 0.246, 0.240, 
0.214. 0.175 

Bl2Sr2Cu06; 0.291, 0.279, 0.247, 
0.241, 0.219, 0.213, 0.177 

Bl2Sr2CaCU208; CuO; Bl2Sr2Cu06 
(trace); 0.387 

Bl2Sr2Cu06; 0.290, 0.283, 0.246, 
0.241, 0.213, 0.177 

Bl2Sr2CaCu208; CuO; Bl2Sr2Cu06; 0.389 

Bl2Sr2CaCu208; Bl2Sr2Cu06; CuO 
(trace); 0.244, 0.213 

Bl2Sr2CaCu208; Bl2Sr2Cu06; CuO 
(trace); 0.244 



TABLE IV. - SUPERCONDUCTING TRANSITION TEMPERATURES FROM 
ELECTRICAL RESISTANCE MEASUREMENTS FOR B1 i .5SrCaCu20x 
GLASS SPECIMENS SUBJECTED TO VARIOUS THERMAL 
TREATMENTS IN AIR 



Sample 


Heat treatment 


Resistive Jq 


Temper- 
ature, 
"■C 


Time, 
h 


Cool 1 ng 


Onset 


R = 


A 


450 


2 


Slow 







B 


450 
560 


2 
2 


Slow 







C 


450 
560 
765 


2 
2 
2 


i Slow 


87 


47 


D 


560 


2 


Slow 







E 


765 


2 


Slow 


82 


38 


F 


845 


88 


Quenched 


88 


11 


G 


845 


88 


Slow 


108. 87 


55 



15 



5.0 



I 2.5 — 




60 170 280 390 500 610 720 830 9t0 1050 1160 1270 

TEMPERATURE, °C 

FIGURE 1. - DTA THERMOGRAM OF Bi^ 5SrCaCU20x GLASS IN 
AIR AT A HEATING RATE OF 10 °C/MIN. 




100 mo 160 190 520 
TEMPERATURE, °C 



550 580 610 



FIGURE 2. - TYPICAL DSC SCAN OF Bi^ 5SrCaCU20 GLASS IN INERT 
ATMOSPHERE AT A HEATING RATE OF 10 °C/MIN. 



600 



TEMPERATURE, "C 
550 500 




FIGURE 3. - PLOTS Of In[TpVa] AGAINST RECIPROCAL OF 
PEAK TEMPERATURE, Tp, FOR THE VARIOUS EXOTHERMS 
OBSERVED IN THE DSC SCANS OF Bl^ 5SrCaCU20^ GLASS. 



102.75 



a 101.50 



2 100.25 



99.00 



SCAN RATE; 
SAMPLE WEIGHT 
ATMOSPHERE: 



5 "C/MIN 
29.052 mg 



101. 71X 



J L_J L 



10 120 200 280 360 110 520 600 680 760 810 

TEMPERATURE, "C 

FIGURE 1. - TGA THERMOGRAM Of Bi., 5SrCaCU20^ GLASS RECORDED 
AT THE HEATING AND COOLING RATES OF 5 °C/MIN UNDER FLOW- 
ING OXYGEN. 



16 



A - Bi2Sr2CuO^ (2201) 
B - Bi2Sr2CaCU20g (2212) 
C - CuO 
U - UNKNOWN 



450 °C, 2h 
+560 °C, 2h 
+765 °C. 2h 



B B 



JjMkxJ'J'^-^^^'^'^*^ 



J L 



J L 



765 °C, 2h 



J 



I I I I I \ \ \ — 1 — 



aA a 



560 °C, 2h 



^ 



A A 



J vJ " W Ui^^.^J^^^^^^'^^ 



J L 



J L 



1__J I 



2^ 25 30 35 W iis 50 55 60 65 70 



20 



F16URE 5 - POWDER X-RAY DIFFRACTION SPECTRA OF Bii ^SrCaCUjO^GLASS SAMPLES 
AMNEALED AT VARIOUS TEMPERATURES AND SLOW COOLED IN AIR. 



A - BljSfjCuOg (2201) 
B - Bi2Sr2CaCU20g (2212) 
C - CuO 
U - UNKNOWN 



FAST QUENCHED 




IGURF 6. POWDER X-RAY DirFRACTION PATTERNS OF Di, 5SrCaClJ20^ Gl ASS 
SPECIMENS ANNEALED AT 8'(5 "C FOR 88 HH AND FAST OUENCHED OR SI OW 
COOLED IN AIR. 



17 




FIGURE 7. - SEM HICROGRAPH OF FRACIURE SURFACE OF A Bi , .SrCaCu,0 
GLASS SPECIMEN ANNEALED AT 150 "c FOR 2 H« IN AIR ANC'SLOH tMLED. 




Ca) CRYSTALLINE. 



(b) GLASSY REGION. 



FIGURE 8. - SEM niCROGRAPHS FROM TWO DIFFERENT REGIONS OF THE FRACTURE SURFACE Of A Bi, 5SrCaCU20^ GLASS SAMPLE HEATED FOR 2 HR EACH AT M50 



ORiGtNAL PAGE 
BLACK AND WHITE "^ VfOGRAPH 



18 




765 °C. 2 h 



O 

inOD ODD 
150 "C, 2 h 
2 h 
2 h 



O 



o 

D 



+ 765 °C. 



aaaa 



AAA 



DC 



aa 



°C, 88 h + SLOW COOL 



100 200 

TEMPERATURE, K 



300 



FIGURE 9. - TEMPERATURE DEPENDENCE OF RESISTANCE OF 
Bii 5SrCaCu0x GLASS SAMPLES ANNEALED AT VARIOUS 
TEMPERATURES AND SLOW COOLED IN AIR. 



x: 1 



D 815 "0/88 h + FURNACE COOL 
O 815 °C/88 h + AIR OUENCH 




100 150 

TEMPERATURE, K 
TEMPERATURE DEPENDENCE OF RESISTANCE, 



FIGURE 10 

NORMALIZED TO ITS VALUE AT 296 K 

GLASS SAMPLES ANNEALED AT 815 °C F0« 88 HR AND 

FUIUI*C£ COOLED OR FAST OUENCHED IN AIR. 



OF Bi.| 5SrCaCU20, 



19 



IVIASA 

National Aeronauttcs and 
Space Adminislration 



Report Documentation Page 



1. Report No. 

NASA CR- 185 139 



2. Government Accession No. 



3. Recipient's Catalog No. 



4. Title and Subtitle 

Superconducting Ceramics in the Bi, 5SrCaCu20, System by 
Melt Quenching Technique 



5. Report Date 
October 1989 



6. Performing Organization Code 



7 Author(s) 

Narottam P. Bansal and Mark R. DeGuire 



8. Pertorming Organization Report No. 
None (E-5064) 



10. Work Unit No. 
307-51-00 



9. Performing Organization Name and Address 

Case Western Reserve University 

Department of Material Science and Engineering 

Cleveland, Ohio 44106 



1 1 . Contract or Grant No. 
NCC3-133 



12. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135-3191 



13. Type of Report and Period Covered 
Contractor Report 
Final 



14. Sponsoring Agency Code 



15 Supplementary Notes 

Project Manager, Martha H, Jaskowiak, Materials Division, NASA Lewis Research Center. Narottam P. Bansal, Case 
Western Reserve University, and NASA Resident Research Associate at Lewis Research Center. Mark R. DeGuire, 
Summer Faculty Fellow at Lewis; present address: Case Western Reserve University. Prepared for the 91st Annual 
Meeting of the American Ceramic Society, Indianapolis, Indiana, April 23-27, 1989. 

16. Abstract 

Bi, sSrCaCu20, has been prepared in the glassy state by rapid quenching of the melt. The kinetics of crystalliza- 
tion of various phases in the glass have been evaluated by a variable heating rate differential scanning calorimetry 
method. The formation of vi"ious phases on thermal treatments of the glass has been investigated by powder 
x-ray diffraction and electrical resistivity measurements. Heating at 450 °C formed Bi2Sr2Cu06, which disappeared 
on further heating at 765 °C, where Bi2Sr2CaCu208 formed. Prolonged heating at 845 °C resulted in the forma- 
tion of a small amount of a phase with T^. onset of ~ 108 K, believed to be Bi2Sr2Ca2Cu30io. This specimen 
showed zero resistivity at 54 K. The glass ceramic approach could offer several advantages in the fabrication of 
the high-T^. superconductors in desired practical shapes such as continuous fibers, wires, tapes, etc. 



17. Key Words (Suggested by Author(s)) 

Superconductor 

Glass-ceramic 

Superconductivity 



18. Distribution Statement 

Unclassified — Unlimited 
Subject Category 76 



19. Security Classif. (of this report) 
Unclassified 



20. Security Classif. (of this page) 
Unclassified 



21 . No of pages 
20 



22. Price* 
A03 



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